JP2004074643A - Method for correcting color shift, optical recording device and image formation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly precisely correct a color shift at low cost without using a driving motor rotation control means or an encoder against a velocity variation of an image carrier or an intermediate transfer member as a dynamic cause. <P>SOLUTION: In the image formation apparatus which images by forming images of different colors by at least one image formation means with the image carrier, and directly or indirectly transferring images of different colors formed by the image formation means onto a moving member, an application position of laser beams emitted from an optical recording means while a latent image is formed by the application of laser beams by the writing means is adjusted in a vertical scanning direction, thereby correcting the color shift between colors. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color misregistration correction method for correcting color misregistration during image formation of a plurality of colors, an optical writing device, and an image forming device. In particular, the present invention relates to a tandem type color copier and a color printer. A plurality of images having different colors sequentially formed by at least one image forming device or a multiplex image forming apparatus provided with a transfer unit, a transfer belt, a sheet on a transfer belt, or an intermediate transfer body to transfer a color image. The present invention relates to a color misregistration correction method for suppressing color misregistration during formation, an optical writing device, and an image forming device.
[0002]
[Prior art]
In recent years, documents processed in offices and the like have rapidly become colorized, and image forming apparatuses such as copiers, printers, and facsimile machines that handle these documents have also been rapidly colored. At present, these color devices tend to have higher image quality and higher speed with higher quality and faster office processing in offices and the like. As a color device that can meet such demands, for example, a so-called tandem type color image forming apparatus having image forming units for each color of black (K), yellow (Y), magenta (M), and cyan (C) is available. Have been proposed and commercialized. A tandem-type color image forming apparatus performs direct or indirect multiple transfer of images of different colors formed by each image forming unit on a transferred transfer material or an intermediate transfer body to form a color image. Things.
[0003]
By the way, the tandem type color image forming apparatus configured as described above is a method of forming one image using a plurality of image forming units, and thus can form a color image at a considerably high speed. . However, if the speed of image formation is increased, the alignment of images formed by the image forming units of each color, that is, color registration (hereinafter referred to as “register”) cannot be adjusted with high accuracy. It has been extremely difficult to achieve both high image quality and high speed. This is because the position and size of each image forming unit of the color image forming apparatus itself, and furthermore, the position and size of components in the image forming unit slightly change. Therefore, an apparatus for forming a color misregistration detection pattern on a transfer member or the like, detecting the pattern with a reading sensor, measuring the amount of color misregistration, and adjusting the image writing timing to reduce the color misregistration is disclosed in Japanese Patent Application Laid-Open No. 2000-2000. 3121 has already been proposed.
[0004]
In this correction method, the position and size of each image forming unit itself and the position and size of components in the image forming unit are delicate due to changes in the internal temperature of the color image forming apparatus and the application of external force to the apparatus. In this case, a color registration deviation (hereinafter, referred to as a “DC color registration deviation”) having a constant magnitude and direction due to the change in the color registration error is detected and corrected.
[0005]
However, in these devices, when an optical deflector of a polygon mirror is used as a writing unit for each color, correction is usually performed in one scanning unit. That is, in the case of an image of 600 dpi, correction is performed in units of about 42 μm, and therefore, strictly, a correction error corresponding to this is included. In order to solve this problem, it is necessary to adjust the rotation phase of each optical deflector while controlling the rotation phase before starting writing the leading edge of the image for each color. Thus, in order to adjust the rotation phase of the optical deflector, the rotation of the optical deflector must be adjusted while temporarily accelerating and decelerating. However, since the optical deflector is rotating at a high speed, Since the phase adjustment takes time and is technically difficult, it is actually very costly. In addition, in order to reduce the cost, in an image forming apparatus that deflects the laser beam of each color with only one deflector, the writing phase of each color is always the same. In the first case, it is theoretically impossible to correct the displacement for one deflection scan.
[0006]
On the other hand, the color registration misregistration (hereinafter referred to as “AC color registration misregistration”) in which, in addition to the DC component, mainly a rotating body such as a photoreceptor or a belt drive roll periodically varies in size or direction that causes a variation. ") Is also included. Japanese Patent Laid-Open No. 2000-199988 describes that the AC color registration shift occurs due to the temporal change (wear) of the belt thickness and the driving roller in the case of a transfer belt.
[0007]
Further, in order to cope with the AC color registration deviation, in a conventional color image forming apparatus, a rotation speed fluctuation of the photosensitive drum is detected by using an encoder attached to a rotating shaft of the photosensitive drum or the like, and the encoder detects the fluctuation. At present, the rotation fluctuation of the photosensitive drum is fed-forward or fed back to the drive motor in order to reduce the rotation fluctuation of the photosensitive drum.
[0008]
[Problems to be solved by the invention]
However, even if the control for reducing the rotation fluctuation of the photoconductor drum or the like is performed based on the detection information from the encoder in this way, the eccentricity of the photoconductor drum itself or the eccentricity of the surface of the photoconductor drum due to the mounting thereof, In the configuration (1), since there is eccentricity due to the clearance error of the photosensitive drum rotating shaft, there is a problem that image quality is deteriorated due to AC color registration misalignment generated due to the eccentricity.
[0009]
Japanese Patent Application Laid-Open No. Hei 9-146329 discloses a configuration in which at least one rotation phase of a rotating body such as a photosensitive drum or a belt drive roll can be individually adjusted to solve such a problem. There has been proposed an invention that suppresses image quality deterioration due to AC color registration deviation caused by a factor. In this proposal, as a method of eliminating the displacement of the AC color registration, the speed of the photosensitive drum, the transfer belt, and the like is controlled, but the cost increases because very precise control and high-precision parts are required. The reality is that we cannot escape.
[0010]
Further, even if this method is used, when the amplitudes of the rotational angular velocities of the respective photosensitive drums are the same, the amount of color misregistration caused by the rotational angular velocities of the photosensitive drums cannot be eliminated. However, since the amplitudes of the fluctuations are not always the same, it is considered that the color shift has not been strictly solved. Further, in order to match the rotation phases of the respective photoconductors, the respective photoconductors are driven independently of each other, so that there is a problem that the cost is increased.
[0011]
Further, a case where the AC color registration deviation is extended when there is a deviation in the thickness of the belt will be discussed. For example, assuming that the diameter of the driving roller of the belt is D (mm), the thickness of the belt is T (mm), and the image forming speed is V (mm / sec), the diameter of the belt neutral surface (diameter of the pitch circle) is
D + T (mm)
Assuming that N is an integer, the distance between each image forming unit is
N × π × (D + T)
Therefore, when making the apparatus the smallest, the distance between each image forming unit is
π × (D + T) (mm)
It becomes.
Assuming that the belt thickness deviation is ΔT, the fluctuation amount of the image forming speed is:
(ΔT) / (T + D) × V (mm / sec) (1)
It is.
[0012]
Usually, since a full-color image is formed by four image forming units, the distance between the farthest image forming units is:
3 × π × (T + D) (mm)
At the original image forming speed,
3 × π × (T + D) / V (second) (2)
It takes time.
Therefore, the amount of image misregistration caused by belt and roller wear can be calculated by multiplying Expressions (1) and (2) between the most distant image forming units.
3 × π × (ΔT) (3)
It becomes.
[0013]
That is, even when the belt thickness deviation is 10 μm, the color shift amount reaches about 94 μm from the equation (3), and a shift exceeding two pixels when the resolution is 600 dpi repeats every belt period. It can be seen that the AC color registration error occurs.
[0014]
As a method of eliminating such an AC color registration deviation, the speed of the transfer belt or the like may be controlled as described above. However, since very precise control and high-precision parts are required, an increase in cost is unavoidable. .
[0015]
The present invention has been made in view of such a situation of the related art, and an object of the present invention is to provide a color misregistration correction method and an optical writing device that can more accurately correct color misregistration in the sub-scanning direction. It is in.
[0016]
Another object is to enable high-precision color misregistration correction at a low cost without using a drive motor rotation control unit or an encoder for the speed fluctuation of the image carrier or the intermediate transfer body, which is a dynamic cause. An object of the present invention is to provide a color shift correction method and an optical writing device.
[0017]
Still another object is to provide an image forming apparatus capable of forming a high-quality image by correcting color misregistration with high accuracy.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the first means visualizes the latent image written on the image carrier by the optical writing means, and directly or indirectly displays the visualized images having different colors on the moving body. In the color misregistration correction method for correcting color misregistration due to misregistration of the image when performing image transfer by performing image transfer, the method includes irradiating a light beam with the light writing unit to form a latent image. The position of the irradiation position of the light beam emitted from the writing means is adjusted in the sub-scanning direction, and the color shift between the colors is corrected. In the first means, the position of the irradiation position of the light beam irradiated from the writing means is adjusted in the sub-scanning direction during the period in which the latent image is formed, and the color shift between the colors is corrected. Can be eliminated.
[0019]
The second means is the first means, wherein the position adjustment of the irradiation position of the light beam in the sub-scanning direction is performed before the adjustment is started. It is performed based on the result of reading the pattern. In the second means, since the position of the irradiation position of the light beam in the sub-scanning direction is adjusted based on the pattern actually written on the image carrier and visualized, the position can be adjusted with high accuracy. .
[0020]
A third means is the second means, wherein timing for writing the pattern is set based on detection timing of a reference point provided on the image carrier. According to the third means, it is possible to eliminate a color shift in which the size and the direction periodically fluctuate due to the rotation speed fluctuation of the image carrier.
[0021]
According to a fourth aspect, in the second aspect, the timing for writing the pattern is set based on the detection timing of a reference point provided on the intermediate transfer member. According to the fourth means, it is possible to eliminate a color shift in which the size and direction periodically fluctuate due to the speed fluctuation of the intermediate transfer body.
[0022]
Fifth means is the first means, wherein the adjustment in the sub-scanning direction includes a step of correcting a writing timing of an optical writing means and a step of correcting a beam position of a light beam. It is characterized by being performed. In the fifth means, the step of correcting the write timing of the optical writing means and the step of correcting the beam position of the light beam are performed in parallel, so that the color shift can be corrected quickly.
[0023]
A sixth means is the fifth means, wherein the step of correcting the write timing corrects a portion corresponding to a quotient obtained by dividing the positional deviation amount by the dot pitch, and the step of correcting the beam position includes correcting the positional deviation amount. It is characterized in that a portion corresponding to the remainder divided by the dot pitch is corrected. In the sixth means, a large positional deviation is performed in the step of correcting the write timing, and a small positional deviation is performed in the step of correcting the beam position. Since the correction of the large positional deviation and the correction of the small positional deviation are independent, The color shift can be corrected with high accuracy.
[0024]
The seventh means is a light writing device which has a plurality of light writing means for irradiating the image carrier with a light beam based on the input image information, and performs light writing for image formation of a plurality of colors. Optical writing is performed on the image carrier, and during the formation of the latent image, the irradiation position of the light beam on the image carrier irradiated from the optical writing unit coincides when the images of the respective colors are superimposed. It is characterized by comprising adjusting means for adjusting in the sub-scanning direction. In the seventh means, the irradiation position of the light beam irradiated from the writing means is adjusted in the sub-scanning direction during the period of forming the latent image, and the irradiation position of the light beam on the image carrier coincides with the superposition of each color. In the sub-scanning direction, the color misregistration whose size and direction periodically fluctuate can be eliminated.
[0025]
In an eighth aspect based on the seventh aspect, the optical writing means includes a laser light emitting element and a coupling optical system, and the adjusting means integrally holds the laser light emitting element and the coupling optical system. It is characterized by comprising a holding member and a drive mechanism for moving the holding member in the sub-scanning direction. In the eighth means, the relative position of the laser light emitting element and the coupling optical system is maintained by moving the holding member that integrally holds the laser light emitting element and the coupling optical system in the sub-scanning direction. In this state, the writing position of the light beam in the sub-scanning direction can be displaced, so that color misregistration can be corrected with a simple structure.
[0026]
A ninth means is the optical device according to the eighth means, wherein the holding member is eccentric with respect to the optical axis of the light beam in an optical housing holding the optical deflector and another optical element for irradiating the image carrier with the light beam. It is rotatably supported on the support shaft in a state where it is set. According to the ninth means, the irradiation position of the light beam can be displaced with a simple structure by rotating with respect to the support shaft, thereby enabling highly accurate correction of color misregistration.
[0027]
A tenth means is the ninth means, wherein the driving mechanism drives the holding member to rotate about the support shaft. In the tenth means, the irradiation position of the light beam can be accurately displaced only by rotating and driving the holding member by the driving mechanism, thereby enabling highly accurate correction of color misregistration.
[0028]
Eleventh means is the ninth means, wherein the eccentric state of the two axes is set such that the optical axis of the light beam and the rotation center axis of the holding member substantially coincide at the light beam deflection position of the light deflector. It is characterized by having been done. In the eleventh means, since the rotation center axis of the holding member and the optical axis of the light beam are substantially coincident with each other at the light beam deflection position of the optical deflector, the optical characteristics change even when the holding member is rotated. There is no. In addition, since the light beam irradiation position of the image carrier does not largely move in the main scanning direction, there is no color shift in the main scanning direction, thereby enabling optical writing for obtaining a high quality image. Become.
[0029]
In a twelfth aspect, in the eighth aspect, the holding member is parallel to the sub-scanning direction of the image carrier on an optical housing that holds an optical deflector and another optical element that irradiates the image carrier with a light beam. And a supporting member movably supported along the guide member. According to the twelfth means, the irradiation position of the light beam can be displaced with a simple structure by moving the holding member along the guide member, thereby enabling highly accurate correction of color misregistration.
[0030]
According to a thirteenth aspect, in the twelfth aspect, the driving mechanism moves the holding member in parallel along the guide member. In the thirteenth means, the irradiation position of the light beam can be accurately displaced only by moving the holding member in parallel by the driving mechanism, thereby enabling highly accurate correction of color misregistration.
[0031]
Fourteenth means is the twelfth means, wherein the curvature of the guide member is set such that the optical axis of the light beam when moved is substantially coincident with the light beam deflection position of the light deflector. Features. In the fourteenth means, the curvature of the guide member is set so that the optical axis of the light beam when moved is substantially coincident with the light beam deflection position of the light deflector. Does not change. Further, since the light beam irradiation position of the image carrier does not move in the main scanning direction, there is no occurrence of color shift in the main scanning direction, thereby enabling optical writing for obtaining a high quality image. .
[0032]
The fifteenth means forms images of different colors by at least one image forming means having an image carrier, and directly or indirectly transfers the images of different colors formed by the image forming means on a moving body. An image forming apparatus for forming an image by transferring an image is provided with an optical writing device according to any one of the seventh to fourteenth means. According to the fifteenth means, optical writing can be performed so as to prevent the occurrence of color shift in which the size and direction periodically fluctuate, so that a high quality image can be obtained.
[0033]
In a sixteenth aspect, in the fifteenth aspect, a plurality of patterns for detecting a color shift of each color are formed on the moving body, and a color shift amount detection is performed based on the formed pattern. Means for adjusting the color shift based on the color shift detected by the color shift detecting means to correct the color shift. In the sixteenth means, since the position adjustment of the irradiation position of the light beam in the sub-scanning direction is performed based on the visualized pattern, the position can be adjusted with high precision, and a high-quality image can be obtained.
[0034]
A seventeenth means is the fifteenth means, wherein a reference position mark provided for detecting a rotation phase of the image carrier, a detection means for detecting the reference position mark, and a detection of the reference position mark Calculating means for detecting a color shift amount of each color on the moving body based on the position and calculating a color shift correction value corresponding to each color, wherein the detected reference position mark and the calculated plurality of color shifts The color shift is corrected by adjusting the light beam irradiation position on the image carrier corresponding to each color during image formation by the adjusting means based on the correction value. In the seventeenth means, the irradiation position of the light beam emitted from the writing means during the formation of the latent image is adjusted in the sub-scanning direction with respect to the color shift due to the rotation speed fluctuation of the image carrier. A color shift in which the size and direction periodically fluctuate due to the fluctuation is eliminated, and a high-quality image can be obtained.
[0035]
An eighteenth means is the fifteenth means, wherein a reference position mark provided for detecting a rotational phase on the moving body, a detection means for detecting the reference position mark, and a detection position of the reference position mark Computing means for detecting a color misregistration amount of each color on the moving body based on the calculated color misregistration correction value corresponding to each of the colors. The color shift is corrected by adjusting the light beam irradiation position on the image carrier corresponding to each color during image formation by the adjusting means based on the values. In the eighteenth means, the amount of color misregistration is accurately detected from the pattern image, the reference position mark of the image carrier is detected at the time of image formation, and an image is formed from the same phase at which the color misregistration was measured. Since the light beam irradiation position on each image carrier is adjusted during the formation of the latent image based on the color shift correction value, the color shift can be accurately and quickly corrected.
[0036]
Nineteenth means is the seventeenth or eighteenth means, wherein the adjusting means emits a light beam onto each image carrier based on a reference position mark of the image carrier and a plurality of calculated color misregistration correction values. A writing timing control circuit for controlling the irradiation timing and a beam position control circuit for controlling the irradiation position of the light beam are provided. In a nineteenth means, an operation of controlling the timing of irradiating each image carrier with a light beam by a timing control circuit based on a color misregistration correction value, and a control of a light beam irradiation position by a beam position control circuit. Since the operations are performed independently and in parallel, quick correction control becomes possible.
[0037]
A twentieth means according to the nineteenth means, wherein a quotient obtained by dividing a positional shift amount by a dot pitch is input to the write timing control circuit, and modulates a laser light emitting element based on the quotient, and the beam position control circuit Is input with a remainder obtained by dividing the displacement amount by the dot pitch, and the optical housing is moved based on the remainder. In the twentieth means, a large displacement corresponding to a quotient is corrected by timing control, and a small displacement corresponding to a surplus is corrected by beam position control. It is corrected, and quick and accurate correction becomes possible.
[0038]
A twenty-first means is the seventeenth or eighteenth means, further comprising a memory for storing the plurality of color shift correction values, and a reading means for reading the stored plurality of color shift correction values. I do. In the twenty-first means, the color misregistration correction value is read from the memory and corrected, so that the color misregistration correction can be repeatedly performed.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that, in the following embodiments, the same reference numerals are given to the same components, and the overlapping description will be appropriately omitted.
[0040]
1. First embodiment
1.1 Schematic configuration of the device
FIG. 1 is a configuration diagram schematically showing a color laser printer as an image forming apparatus according to the present embodiment, FIG. 2 is a plan view of an optical writing (exposure) device, and FIGS. 3 and 4 are schematic diagrams of an optical writing (exposure) device. FIG.
[0041]
In FIG. 1, a color laser printer 1 as an image forming apparatus employs an electrophotographic image forming process, and basically includes an image forming apparatus 2, a sheet feeding device 3 including a sheet feeding cassette, and a fixing device 4. Have been. The image forming apparatus 2 includes a photoconductor drum 10, an exposure unit 6, a transfer unit 5, and the like. A plurality of photoconductor drums 10 (10Y, 10C, 10M, and 10K) are provided with a charging unit 8 (8Y, 8Y, 8C, 8M, 8K), exposure unit 6 (6Y, 6C, 6M, 6K), developing unit 9 (9Y, 9C, 9M, 9K), transfer unit 5 (5Y, 5C, 5M, 5K), cleaning unit 7 ( 7Y, 7C, 7M, 7K). Hereinafter, the description will be generally given with only the reference numerals, and when it is necessary to touch the elements for each color, the description will be given with Y, C, M, and K added to the reference numerals.
[0042]
The charging unit 8 includes a conductive roller formed in a roller shape, and supplies a charging bias voltage to the roller from a power supply device to uniformly charge the photosensitive layer on the surface of the photosensitive drum 10. The exposure unit 6 irradiates a laser beam (hereinafter, referred to as a laser beam L (LY, LC, LM, LK)) to be turned on / off based on the image data onto the surface of the photoconductor drum 10, and An electrostatic latent image is formed. The developing unit 9 includes a developing roller and a developer accommodating section, and visualizes an electrostatic latent image on the photosensitive drum 10. A color image forming apparatus often has four developing means of three colors of yellow Y, cyan C, and magenta M and black K for forming a color image like a color laser printer. In the present embodiment, as shown in FIG. 1, four image forming units of yellow Y, cyan C, magenta M, and black K are provided from the left of the figure (from the upstream side in the rotation direction of an intermediate transfer belt described later). Have been. However, since a full-color image can be formed even with three colors of yellow Y, cyan C, and magenta M excluding black, the image forming apparatus can be configured without black K.
[0043]
The transfer unit 5 transfers an image visualized by toner on the photosensitive drum 10 from the photosensitive drum 10 to an intermediate transfer belt 11 as an intermediate transfer body by a transfer roller 12. The intermediate transfer belt 11 is stretched between a driving roller 34, a driven roller 36, and a pressing roller 35 as shown in FIG. 9 described later, so that the driving roller 34 rotates in the direction of arrow A in the drawing. Accordingly, it moves in the direction B in the figure. The toner image formed on each photoconductor drum 10 comes into contact with the intermediate transfer belt 11 and a predetermined bias voltage is applied to a transfer roller 12 (12Y, 12C, 12M, 12K) disposed on the back surface of the intermediate transfer belt 11. Is transferred onto the intermediate transfer belt 11. Such transfer is generally called primary transfer, and such a transfer unit 5 is also called primary transfer unit. The cleaning unit 7 removes the developer remaining on the photosensitive drum 10 after the transfer to the intermediate transfer belt 11 before the next image forming operation.
[0044]
The transfer method of such a color image forming apparatus is roughly classified into the following two methods. One is a method in which images formed by a plurality of photosensitive drums 10Y, 10C, 10M, and 10K are superimposed on the intermediate transfer belt 11 and then transferred to a transfer material (this is referred to as secondary transfer). So-called intermediate transfer type. The other is a so-called direct transfer system in which images formed on the photosensitive drums 10Y, 10C, 10M, and 10K are directly transferred to a transfer material and are superimposed on the transfer material. The color laser printer 1 shown in FIG. 1 is of the former type.
[0045]
In the intermediate transfer method described in the present embodiment, images superimposed on the intermediate transfer belt 11 are collectively transferred onto a transfer material by a transfer roller 13 as a transfer unit (referred to as a secondary transfer unit). The transfer material is often a recording material such as paper (hereinafter, also referred to as transfer paper), and is stored in the paper feed cassette 3a of the paper feed device 3 described above. The transfer paper is separated and conveyed one by one by the pickup roller 3b. The transfer paper separated and conveyed one by one by the pickup roller 3b is conveyed to the transfer roller 13 as the secondary transfer means by the paper feed roller 3c, where the full-color toner superimposed on the intermediate transfer belt 11 there. The image is transferred to transfer paper. After that, in order to fix the image, the transfer paper is conveyed to the fixing device 4 and heated and pressed by the fixing device 4 to fix the image. Further, the sheet is discharged from the sheet discharging roller 3e to the outside of the apparatus via the conveying roller 3d.
[0046]
In the case of direct transfer, the recording paper constitutes the moving body, and in the case of indirect transfer, the intermediate transfer body (intermediate transfer belt 11) constitutes the moving body.
[0047]
1.2 Exposure unit (optical writing device)
FIG. 2 shows the internal structure of the exposure unit 6 in detail. As can be seen from FIG. 2, the basic configuration of the exposure unit 6 includes a laser light source (unit) 61 that oscillates a laser beam L and a deflection scanning unit that deflects and scans the laser beam L modulated based on an image signal. A polygon mirror 62, an imaging optical system 63 for imaging the laser beam L deflected and scanned to a desired size on the photosensitive drum 10, and synchronization as a synchronization detecting means for detecting the timing of starting scanning of the laser beam L. And a detection unit 64. The polygon mirror 62 is driven to rotate at high speed by a polygon motor 62a. In the present embodiment, four laser light sources 61Y, 61M, 61C and 61K are mounted to irradiate the laser beam L to the four photoconductors 10 of Y, C, M and K, and two light sources 61Y and 61C are provided. And a so-called opposing scanning method in which the light is incident on both sides of the polygon mirror 62 separately into 61M and 61K.
[0048]
In the present embodiment, a semiconductor laser (LD) 61a is used as a light-emitting source, and the semiconductor laser 61a, a collimating lens 61b for substantially collimating divergent light emitted from the semiconductor laser 61a, and a semiconductor laser driving circuit board 61c. A laser light source unit (LD unit) 61 is constituted by the holding member (base) 61d for holding these. The laser beam L emitted from the LD unit 61 reaches the polygon mirror 62 through the aperture 65 and the cylinder lens 66 as can be seen from FIG. In order to make the two laser beams LY, LC and LM, LK independently incident on the polygon mirror 62 from one side, mirrors 67a, 67b are arranged on one optical path as shown in FIG.
[0049]
When the rotation speed of the polygon mirror 62 is high enough to exceed 30,000 rpm, soundproof glass is often used in front of the polygon mirror 62 for noise control or the like. In the figure, a soundproof glass 68 is provided on both sides of the polygon mirror 62.
[0050]
The laser beam L deflected and scanned by the polygon mirror 62 again passes through the soundproof glass 68 and enters the imaging lens 63. Thereafter, the laser beam L guided to the photosensitive drum 10 reaches the photosensitive drum 10 via the mirror 69. The irradiation angle with respect to the surface of the photosensitive drum 10 is set to be substantially the same for each of the Y, C, M, and K colors. On the other hand, for synchronization detection for determining the timing of starting writing, the laser beam L passing through the imaging lens 63 is turned back by the synchronization detection mirror 64a to reach the synchronization detection unit 64. The synchronization detector 64 includes an imaging lens 64b, an electric circuit board 64c having a photoelectric element, and a holding member 64d for holding them.
[0051]
Since the original meaning of the synchronization detection is to take the timing of the scanning light, it is sufficient that the synchronization detection is provided prior to the normal scanning. However, in this embodiment, a change in the speed (or time) of one scanning is detected. For this purpose, a detecting means is also provided at the end of scanning. FIG. 2 shows a configuration for synchronizing before and after this scanning. In this example, one synchronization detection unit 64 detects the upper and lower scanning beams.
[0052]
FIGS. 3 and 4 show an example of a configuration in which a single light deflector emits laser light to all of the plurality of photosensitive drums 10Y, 10C, 10M, and 10K. The difference between the two is that the polygon mirror 62 is composed of one or two polygon mirrors. Both have their strengths and weaknesses, and either one can be adopted. Although not shown in the figure, individual exposure means can be provided for each of the plurality of photoconductors. For example, it is also possible to adopt a configuration in which four exposure means are respectively arranged on four photoconductors to perform optical writing. In FIGS. 3 and 4, dustproof glasses 60Y, 60C, 60M, and 60K are provided at the exit from the exposure unit 6 to the photosensitive drum 10 in order to prevent dust from entering the exposure unit.
[0053]
1.3 Beam irradiation position adjustment mechanism
As a method for displacing the laser beam irradiation position in the sub-scanning direction, as shown in FIG. 5, an LD unit 61 including a semiconductor laser 61a and a holding member 61d for holding a collimating lens (coupling optical system) 61b is moved in the sub-scanning direction. There is a method of moving the laser irradiation position on the photoconductor surface 10a of the photoconductor drum 10 by displacing. The example shown in FIG. 5A is an example in which the LD unit 61 is moved in parallel (upward in the figure), and the example shown in FIG. This is an example in which the angle has been adjusted so that the angles coincide on the mirror surface 62b of the polygon mirror 62.
[0054]
As another method, there is a method of displacing the turning mirror 69 in the optical writing device to displace the beam irradiation position. However, since the irradiation position largely moves due to a small angle change, there is a problem in terms of accuracy in practice. There is not practical. Alternatively, a sheet glass-like object may be inserted into the polygon mirror 62 on the upstream side of the incident laser beam L at an angle to the laser beam L, and the angle may be changed to move the beam position in the sub-scanning direction. it can. However, depending on the number of components and the surface accuracy of the glass sheet, there is a risk of adversely affecting the beam imaging performance. However, whichever method is employed, it is sufficient if the beam position of the laser beam L can be accurately controlled. . These examples will be described later.
[0055]
For this reason, in the present embodiment, the position adjusting device of the holding member 61 is configured as shown in FIG. FIG. 7 is a front view of the position adjusting device according to the present embodiment, and is a view of the LD unit 61 of FIG. 7 viewed from the emission side of the laser beam L. That is, a semiconductor laser (LD) 61a is used as a light emitting source, and this semiconductor laser 61a, a collimating lens 61b that makes the divergent light emitted from the semiconductor laser 61a substantially parallel, a semiconductor laser driving circuit board 61c, A laser light source unit (LD unit) 61 is composed of a holding member (base) 61d for holding. An arm portion 61e extends in a direction corresponding to the main scanning direction of the holding member 61d, and a lower portion of the arm portion 61e in the drawing is driven by a beam position moving motor 70 composed of a stepping motor and the beam position moving motor 70. A lead screw 71 is provided, and the amount of advance and retreat of the lead screw 71 is controlled according to the rotation angle (the number of steps) of the beam position moving motor 70. The lead screw 71 is provided so as to rotate integrally and coaxially with the rotation axis of the beam position moving motor 70, and is screwed to a screw portion 61i provided on the arm portion 61e to control the rotation operation of the lead screw 71 to the arm portion. The operation is converted into the advance / retreat operation (rotation operation in this case) of 61e.
[0056]
As shown in FIG. 7, the holding member 61 is rotatably supported about a rotation center axis 61f near the position where the collimator lens 61 is provided, and the laser beam L emitted from the collimator lens 61 according to the position of the arm 61e. The position of the optical axis 61g moves. Therefore, the beam position of the laser beam L defined by the optical axis 61g on the photoreceptor surface 10a can be accurately moved in units of microns according to the rotation of the beam position moving motor 70. FIG. 8 is an explanatory diagram showing a beam position on the photoconductor surface 10a at this time. The rotation of the holding member 61d about the rotation center 61f causes the rotation around the rotation center 10b on the photoconductor surface 10a. Move in the scanning direction.
[0057]
In FIG. 8, the beam irradiation position (beam spot position) on the photoconductor surface 10a by the laser beam L emitted from the LD 61a is shifted from the rotation center 61f when the optical axis 61g of the laser beam L is displaced in the main scanning direction. The beam irradiation position which is the farthest position is indicated by hatching. The beam irradiation positions indicated by broken lines above and below the beam irradiation positions indicate the respective beam irradiation positions after being displaced in the sub-scanning direction when the optical axis 61g is displaced around the rotation center 61f. The position of the LD 61b when the correction value of the beam irradiation position is 0 may be set to the hatched beam irradiation position shown in FIG. 8 formed by the laser beam L emitted therefrom.
[0058]
That is, in this embodiment, in order to accurately move the beam position of the laser beam L in the sub-scanning direction in units of microns, the holding member 61 holding the laser light emitting element (LD 61a) and the coupling optical system (collimating lens 63) is used. The LD unit 61 is rotatably mounted on an optical housing that holds a polygon mirror 62 and other optical elements that irradiate the photosensitive drum 10 with the laser beam L, and a rotation center axis 61f of the LD unit 61 and the laser beam L. The optical axis 61g is provided with a predetermined interval (shift) G mainly in the main scanning direction. Then, at the laser beam deflection position on the mirror surface 62b of the polygon mirror 62, the rotation center axis 61f of the LD unit 61 and the laser optical axis 61g are substantially coincident with each other, and the aperture 65 for shaping the shape of the laser beam L fixed to the optical housing is formed. On the other hand, the configuration is such that the LD unit 61 is rotated. With this configuration, even when the LD unit 61 is rotated, the luminous flux passing through the aperture 65 and thereafter does not greatly change, so that control can be performed in units of several μm on the photoconductor surface 10a.
[0059]
Generally, an aperture 65 for shaping the beam shape is often attached to the LD unit 61. However, when the aperture 65 is attached to the LD unit 61 and the LD unit 61 is displaced, the beam position on the photoconductor surface 10a is changed. It moves largely in the sub-scanning direction and is not suitable for position control in units of several μm. That is, in the case of an apparatus that adjusts the beam position by largely moving the beam position, a configuration in which the aperture 65 is attached to the LD unit 1 may be used. However, in an apparatus that needs to be adjusted in units of several μm as in the present embodiment, The aperture 65 needs to be provided separately from the LD unit 61.
[0060]
1.4 Driving mechanism of photosensitive drum and intermediate transfer belt
FIG. 9 is a view schematically showing a rotation drive mechanism of the photosensitive drums 10Y, 10C, 10M, and 10K of the image forming unit 2 and the intermediate transfer belt 11 in FIG. As described above, the intermediate transfer belt 11 is stretched between the driving roller 34, the driven roller 36, and the pressure roller 35, and is driven by the belt driving motor 30. The belt drive motor 30 is coaxially attached to the drive shaft of the belt drive motor 30 and is stretched between a motor pulley 31 that rotates integrally and a drive pulley 33 that is provided coaxially with the drive roller 34 and rotates integrally. The belt drive roller 34 is driven via the timing belt 33 thus set, and thus the intermediate transfer belt 11 is rotationally driven.
[0061]
The photoconductor drums 10Y, 10C, 10M, and 10K provided for each color are in contact with the transfer surface (surface) of the intermediate transfer belt 11 and are provided coaxially with the photoconductor drums 10Y, 10C, 10M, and 10K. The body gears 21Y, 21C, 21M, and 21K are rotationally driven by being connected and driven by rotational connection gears (idler gears) 22a and 22b provided at two locations. A drive motor gear 20, which is coaxially attached to the rotation shaft of the drum drive motor 19 and rotates integrally, meshes with the respective photoconductor gears 21C and 21M of the photoconductor drum 10C for cyan and the photoconductor drum 10M for magenta, One of the rotational driving forces is transmitted to the photoreceptor gear 21Y of the yellow photoreceptor drum 10Y via the photoreceptor gear 21C of the photoreceptor drum 10C for cyan and the rotational connection gear 22a, and the other is supplied to the photoreceptor gear for magenta. The power is transmitted to the photoconductor gear 21K of the photoconductor drum 10K for black via the photoconductor gear 21M of the drum 10M and the rotary connection gear 22b. Thus, the four photosensitive drums 10Y, 10C, 10M, and 10K can be synchronously driven in the same direction by one motor 19. The diameter and the number of teeth of each of the gears 21Y, 21C, 21M, and 21K, and the diameter and the number of teeth of the rotary connection gears 22a and 22b are set to be the same, whereby the four photosensitive drums 10Y, 10C, 10M, and 10K are driven at the same peripheral speed.
[0062]
In the present embodiment, a color misregistration detection sensor 38 is provided downstream of the belt drive roller 34 in the rotation direction of the intermediate transfer belt 11, and detects color misregistration (position misregistration) at this position. The color misregistration detection sensor 38 detects a color misregistration by detecting a color misregistration detection pattern (image) PN formed on the intermediate transfer belt 11. More specifically, in order to obtain data on which color misregistration is corrected, a color misregistration detection pattern (image) PN as shown in FIG. 10A is created on the intermediate transfer belt 11 and is used for color misregistration detection. The color misregistration data is obtained by detecting with a resolution of about 5 μm by the sensor 38. The color misregistration detection pattern PN is a line image of a fixed length along the main scanning direction spaced at a predetermined interval in the sub-scanning direction, and is formed by the photosensitive drums 10Y, 10C, 10M, and 10K for each color. The predetermined interval is given by the calculated times t1, t2, and t3 (FIG. 10B), assuming that the speeds of the photosensitive drum 10 and the intermediate transfer belt 11 are set values. Actually, the interval between them changes due to speed fluctuations or the like. Therefore, the amount of the change is detected and the color shift (registration) fluctuation is detected by comparing with a reference value. Since the color shift is caused by the position shift of the writing position, in this embodiment, the color shift and the position shift are used synonymously unless otherwise specified.
[0063]
The causes of the fluctuations in the rotation speed of the photoconductor drum 10 include uneven rotation of the drive motor 19, the accumulated pitch error and eccentricity of the drive motor gear 20, the accumulated pitch error and eccentricity of the photoconductor gear 21, and the rotation coupling gears 22 a and 22 b. , The rotation speed of the photosensitive drum 10 varies. In the present embodiment, the driving mechanism is constituted by the gear train, and therefore the gear is described. However, the same applies to the case where the pulley is used. As described above, the rotation speed of the photosensitive drum 10 fluctuates due to each driving element, and the AC color registration deviation that fluctuates periodically occurs.
[0064]
As described above, the driving of the intermediate transfer belt 11 in the indirect transfer system or the transfer conveyance belt in the direct transfer system is transmitted by the timing belt 32 stretched between the motor pulley 31 and the roller driving pulley 33. In this case, too. Factors that cause the speed variation of the intermediate transfer belt 11 include uneven rotation of the belt drive motor 30, eccentricity of the drive motor pulley 31, eccentricity of the roller drive pulley 33, eccentricity of the belt drive roller 33, and belt thickness deviation. Causes an AC color registration shift.
[0065]
FIG. 11 is a graph in which the color misregistration detection pattern PN is formed, and the color misregistration detection sensor 38 measures the AC color registration misregistration. This figure shows the shift amount of the cyan image C with reference to the black K. As described above, in practice, a color shift due to a speed variation of the intermediate transfer belt 11 or the photosensitive drum 10 occurs, and a DC color registration shift may be superimposed. Here, a color shift of 20 μm in one direction corresponds to a DC color registration shift, and the AC color registration shift is superimposed on this shift amount.
[0066]
1.5 Position shift correction control
FIG. 12 is a block diagram showing a control configuration for performing the displacement correction control. The control circuit includes a registration controller 100 and a system controller 200. The registration controller 100 includes a color misregistration amount calculation circuit 110, a color misregistration correction value calculation circuit 120, a sensor control circuit 130, a counter Y140Y for each of Y, M, and C, a counter M140M, and a counter C140C. , The counters Y140Y, M140M, and C140C are input to the color shift amount calculation circuit 110. The sensor control circuit 130 controls the above-described color misregistration detection sensor 38, and the detection output of each color of the color misregistration detection sensor 38 is input to the counters Y140Y, M140M, and C140C for each color. The color shift correction value calculation circuit 120 is provided with a memory 121 for storing the color shift correction values.
[0067]
The system controller 200 includes a beam position control circuit 210, a motor driver 220, a write timing control circuit 230, and an LD modulation circuit 240. The beam position control circuit 210 drives the beam position moving motors 70Y, 70M, and 70C for moving the beam positions of the Y, M, and C color LD units 61 via the motor driver 220. The write timing control circuit 230 includes an LD modulation circuit. The LDs 61aY, 61aM, 61aC, and 61aK that perform writing of each color are modulated via 240.
[0068]
1.5.1 Color shift correction value creation
As shown in FIG. 12, when correcting color misregistration, a color misregistration correction value (registration misregistration correction value) is obtained, and correction is performed based on this correction value. Therefore, the color misregistration detection pattern PN shown in FIG. 10 is written on each photosensitive drum 10 to visualize the image, and is transferred onto the intermediate transfer belt 11. Then, the color misregistration detection sensor 38 detects the color misregistration based on a preset color. Measure the amount. In the present embodiment, K1i, K2i, and K3i are calculated on the basis of black K. Hereinafter, the registration correction value creation routine will be described with reference to the flowchart in FIG.
[0069]
In this routine, as a first process (step S101), the color misregistration detection pattern PN is written on the photosensitive drums 10Y, 10C, 10M, and 10K (step S102), developed, and transferred onto the intermediate transfer belt 11 (step S103). ). Then, the color shift detection pattern PN is read by the color shift detection sensor 38 (step S104). At this time, as shown in FIG. 12, the output intervals of the color misregistration detection sensor 38 are counted by the respective counters 140Y, 140M, 140C for each color, and the time t1, t2, t3 shown in FIG. The color shift amounts K1i, K2i, and K3i are calculated from this time (step S105), and the color shift correction values (values converted into the number of motor rotation steps of the beam position moving motor 70 of the LD unit 61) D1i, D2i. , D3i are calculated by the color misregistration correction value calculation circuit 110 (step S106), and correction values other than the reference color are stored in the memory 121 (step S107). The correction values D1, D2, and D3 are compared with the determination value A (step S108). If the correction values D1, D2, and D3 are larger than the determination value A (step S108-N), the beam position is adjusted again based on the correction values D1, D2, and D3. While forming a color shift pattern (steps S109 → S110 → S102), color shift correction values D1i, D2i, D3i are newly calculated (steps S103, S104, S105, S106). And so on.
Correction value D1 = D11 + D12 + ...
Correction value D2 = D21 + D22 + ...
Correction value D3 = D31 + D32 + ...
Then, when the value of each Dni (n, i: a positive integer) becomes equal to or smaller than the determination value A (step S108-Y), the operation of creating the color misregistration correction value is terminated and stored in step S107. The color shift correction value Dn is stored in the memory 121.
[0070]
1.5.2 Correction of color shift during image formation
FIG. 14 is a flowchart illustrating a processing procedure of a correction process for correcting a color shift during image formation.
[0071]
After the color shift correction value Dn is created as described above, the color shift is corrected using the color shift correction Dn to form an image. That is, when image formation is started, the measured color shift correction value Dn is called from the memory 121 (step S201), and the color shift correction value Dn at the leading end of the image is decomposed into a timing control correction value and a beam position correction value (step S201). Step S202). The reason why the timing control correction value and the beam position correction value are decomposed is that the beam position control circuit 210 and the write timing control circuit 230 of the system controller 200 perform processing as can be seen from the block diagram of FIG. This decomposition divides the color shift amount at the leading end of the image by a value corresponding to one line interval to obtain a “quotient” and its “remainder”. The “quotient” is input to the write timing control circuit 230, and the “remainder” Is input to the beam position control circuit 210. In other words, "quotient" corresponds to writing timing correction, and "remainder" corresponds to beam position correction. The reason is that it takes time to move the beam position largely by the motor 70, but when the timing is controlled, a large color shift amount can be corrected instantaneously.
[0072]
When the color misregistration correction value is calculated in this manner, the system controller 200 executes the beam position correction control and the write timing correction control, and starts writing with the correction write position corrected by these correction processes. Image formation is performed (step S203). Since the amount of color misregistration after the leading end of the image changes smoothly without abrupt change, color misregistration correction is performed by correcting the beam position to form an image (step S203). In this manner, the color misregistration correction value at the leading end of the image can be decomposed, and an image can be formed at the corrected image position from when the reference position of the photosensitive drum 10 is detected. Then, the image forming is executed by performing the color shift correction.
[0073]
As shown in FIG. 12 described above, the beam position control circuit 210 sends a signal corresponding to the displacement amount for correction to the beam position moving motor 70 shown in FIG. 7 based on the color shift amount correction value Dn. When the output is performed and the motor is driven to rotate, and the LD unit 61 is rotated about the rotation center 61f, the optical axis 61g of the laser beam L is displaced as shown in FIG. 6, and as shown in FIG. Above, the beam irradiation position is displaced. In this embodiment, as a result of measuring the rotation angle of the LD unit 61 and the beam irradiation position on the photoconductor surface 10 by using a stepping motor of 20 pulses per rotation as the beam moving motor 70, the beam position on the photoconductor surface 10a is 40 μm / 1 rotation (approximately 2 μm per pulse), and could be controlled with very high accuracy. That is, when the writing density is 1200, since the dot pitch is about 21 μm, color shift can be corrected with an accuracy of 1/10 of the dot pitch.
[0074]
As shown in FIG. 8, in the present embodiment, the beam position of the laser beam L is also displaced in the main scanning direction by the rotation of the LD unit 61, but the displacement is smaller than the displacement in the sub-scanning direction. Since the writing is performed in the main scanning direction by the synchronization detecting unit 64, no problem occurs.
[0075]
1.5.3 Details of positioning control
The details of the alignment of the images of each color performed in the color laser printer 1 according to the present embodiment will be described.
[0076]
In the color laser printer 1, the image forming apparatus 2 forms and writes Y, C, M, and K on the photosensitive drums 10Y, 10C, 10M, and 10K for the Y, C, M, and K by the exposure unit 6 for each color. A color misregistration detection pattern PN of each color of K is formed on the intermediate transfer belt 11 as shown in FIG. The measurement pattern PN of each color is formed outside the area of the intermediate transfer belt 11 where the transfer paper is transported. Each color misregistration detection pattern PN is formed after t1, t2, and t3 hours on the basis of black K in the order of K, M, C, and Y in the direction indicated by the arrow that is the transport direction of the intermediate transfer belt 11, and at this time interval, the intermediate transfer is performed. It is formed as a linear pattern extending in a direction substantially perpendicular to the conveying direction of the belt 11. The color misregistration detection patterns PN are sequentially detected optically when passing below the color misregistration detection sensor 38 as the intermediate transfer belt 11 moves in the direction indicated by the arrow, and are counted by the counters 140Y, 140M, and 140C for each color. Is counted. The count value is input to the color misregistration amount calculation circuit 110, and by comparing the times t1, t2, and t3 written based on black K with the detected time, the misregistration amount in the sub-scanning direction between the colors can be calculated. .
[0077]
The counters 140Y, 140M, 140C are all reset by the K detection signal and start counting. Then, for example, the counter 140C stops counting according to the C detection signal. The other counters 140M and 140Y stop counting in response to the M and Y detection signals, respectively. Since the operations of the following circuits are the same for Y, M, and C, C will be described as a representative. In this embodiment, as described above, the image of each color is aligned with reference to the position of the K pattern PN, and the calculation is performed by setting the clock frequency of the counter to M (Hz) and the actual count value. Where KC is the set value of the count value and KCs is the difference between the set value TKC = KCsM.
ΔTC = KCM−KCsM
Is calculated. This ΔTC represents the amount of deviation of the interval between the K measurement pattern image and the C measurement pattern image from the set interval.
[0078]
Here, in the case where the polygon mirror 62 shown in FIG. 6 has, for example, six polygon surfaces 62b serving as reflection surfaces, is rotated at 20,000 rpm, and an image having a pixel density of 600 dpi is formed by the single beam LD 61a. The image is formed by setting the linear speed V1 of the photosensitive drum 10 to 84.67 mm / s. If writing is performed with two beams, the linear velocity of the photosensitive drum 10 is 169.33 mm / s. Here, for example, when the shift amount ΔTC of the K and C measured pattern images with respect to the set interval is calculated to be 4.8 ms, the beam irradiation position adjustment value ΔX becomes:
ΔX = ΔTC × V1
= 4.8 ms × 84.67 mm / s
= 0.406mm
It becomes. The beam position control circuit 210 drives the motor 70 for displacing the optical axis 61g of the laser beam based on this value, and displaces the irradiation position of the laser beam on the photosensitive drum 10 by 0.406 mm in the sub-scanning direction. Then, the deviation amount is corrected. Similarly, for each of the M and Y color shift detection patterns PN, the shift amounts ΔTM and ΔTY are calculated, and the shift amounts are corrected by displacing the optical axis 61g of the laser beam according to the shift amounts.
[0079]
By performing such control, in the laser beam printer 1, even if the rotation phases of the respective polygon mirrors 62 do not match, it is possible to strictly correct the displacement amount. Although not shown here, such a correction can be similarly applied to a color image forming apparatus that writes an image of each color using a single LD unit and an optical deflector. As a result, precise alignment can be performed.
[0080]
As described above, according to the present embodiment, the color misregistration detection pattern PN is written prior to image formation, the visualized color misregistration detection pattern is read, and based on the beam position correction data from the read color misregistration detection pattern PN. During the latent image formation, the beam position changing motor 70 is rotated to correct the writing position of the color having the color shift in the sub-scanning direction, so that the position shift can be corrected with high accuracy.
[0081]
2. Second embodiment
2.1 Schematic configuration and control configuration of device
In this embodiment, as shown in FIG. 15, a photoconductor reference position mark 23 is provided on one of the photoconductor drums 10 in the first embodiment, and this photoconductor reference position mark 23 is detected by a reference position detection sensor 24. The first embodiment differs from the first embodiment only in that control is performed based on the sensor output of the photoconductor reference position mark 23 and the reference position detection sensor 24. Therefore, the same reference numerals are given to the same parts, and the duplicate description will be omitted.
[0082]
FIG. 15 is a diagram schematically illustrating a rotation drive mechanism of the photosensitive drums 10Y, 10C, 10M, and 10K and the intermediate transfer belt 11 of the image forming unit 2 according to the present embodiment. As can be seen from FIG. 15, in the rotary drive mechanism of the first embodiment shown in FIG. 9, a photoconductor reference position mark 23 is provided on a photoconductor gear 21C for driving a photoconductor drum 10C for cyan C, and image formation is performed. A photoconductor reference position detection sensor 24 is provided on the housing side of the unit 2. Further, a photoconductor reference position detection sensor 24 is provided as shown in a block diagram showing a control configuration for performing the displacement correction control in FIG. The photoconductor reference position detection sensor 24 is controlled by a sensor control circuit 130, and a sensor output is input to the sensor control circuit 130, and is controlled as shown in FIGS.
[0083]
The block diagram shown in FIG. 17 is the same as the first embodiment except that the photoconductor reference position detection sensor 24 is added to the control configuration for performing the position shift correction control shown in FIG. The same reference numerals are given to the respective units, and the duplicate description will be omitted.
[0084]
As shown in FIG. 15, when the photoconductor drums 10Y, 10C, 10M, and 10K are connected to the photoconductor gears 21Y, 21C, 21M, and 21K by rotating body connection gears 22a and 22b, gears are assembled. Since the phases of the photoconductor gears 21Y, 21C, 21M, and 21K do not deviate from the later initial state, any one of the predetermined photoconductor drums 10Y, 10C, 10M, and 10K or the photoconductor gears 21Y, 21C, 21M, and 21K. A reference position mark 23 and a photoconductor reference position detection sensor 24 for detecting the reference position mark 23 are provided to detect the rotational phase of the drum. When each of the photoconductor drums 10Y, 10C, 10M, and 10K is driven to rotate by an independent motor without using the configuration as in this embodiment, each of the photoconductors 10Y, 10C, 10M, and 10K or the photoconductor is used. A reference position mark 23 and a reference position detection sensor 24 for detecting the reference position mark 23 may be provided on the gears 21Y, 21C, 21M, and 21K to detect the rotational phase.
[0085]
As described above, the rotation speed fluctuation of the photoconductor is caused by the uneven rotation of the drive motor 19, the accumulated pitch error and eccentricity of the drive motor gear 20, the accumulated pitch error and eccentricity of the photoconductor gear 21, and the rotation connection (idler). The rotation speed of the photosensitive drum 10 fluctuates due to the accumulated pitch error and eccentricity of the gears 22a and 22b. Although the present embodiment has been described with gear drive, the same applies to the case where a pulley is used. As described above, the rotation speed of the photoconductor is changed by each driving element, and the AC color registration shift that fluctuates periodically occurs.
[0086]
Therefore, in the present embodiment, in order to reduce the displacement of the AC color registration due to the rotation speed fluctuation of the photosensitive drum 10, the relationship between the rotation angle θ from the exposure to the transfer position and the rotation speed of the driving element is related as follows. I have.
(1) Transfer position interval = integer multiple of the distance between exposure and transfer position
{Circle around (2)} Rotation angle θ from exposure to transfer position = motor rotates an integer
(3) Rotation angle from exposure to transfer position θ = idler rotates integer
If these three conditions are satisfied, the rotation unevenness of one rotation of the drum drive motor 19 and the speed fluctuations related to the motor gear 20 and the idler gears 22a and 22b may be different from the color misregistration because the period is synchronized between the exposure and the transfer. No. However, only the photoreceptor gear 21 cannot be synchronized because it is longer than the period between the exposure and the transfer, causing the AC color registration deviation. However, if the phase and the amplitude of each of the photoconductor gears 21Y, 21C, 21M, and 21K are made the same, the AC component position deviation can be eliminated, but in reality, the amplitudes cannot be said to be the same, so that the An AC component position shift as shown in FIG. 16 will occur.
[0087]
FIG. 16 is a graph in which a color misregistration detection pattern is formed at a time when the photoconductor reference position mark 23 is detected by the photoconductor reference position detection sensor 24, and the AC color registration misregistration is measured by the color misregistration detection sensor 38. Here, the deviation amount of the cyan image is shown with reference to black K. As described above, a color shift due to a period change of one rotation of the photosensitive drum 10 occurs, and a DC color registration shift (20 μm in the figure) may be superimposed.
[0088]
2.2 Creating color shift correction values
FIG. 18 is a flowchart illustrating a processing procedure for creating a color misregistration correction value according to the present embodiment.
[0089]
In this routine, a process of detecting the photosensitive member reference position (step S120) is provided between steps S101 and S102 in the flowchart of FIG. 13 in the first embodiment, and the photosensitive member reference position detection sensor 24 described above detects the photosensitive member. At the time when the reference position mark 23 is detected (or based on this time), the color misregistration correction pattern PN is written (step S102). Since the respective processing steps except for the step S120 are the same as those in the first embodiment, duplicate description will be omitted.
[0090]
2.3 Correction of color shift during image formation
FIG. 19 is a flowchart illustrating a processing procedure for correcting a color shift in the second embodiment. In this flowchart, the photoconductor reference position detection process (step S210) is performed between step S202 and step S203 in the flowchart of FIG. 14 in the first embodiment, and the other processing steps are the first process. This is the same as the embodiment. That is, after the color shift correction value Dn is created as described above, the color shift is corrected using the color shift correction Dn to form an image. In this embodiment, as described above, the photoconductor reference position mark 23 is detected by the photoconductor reference position detection sensor 24, and at the time when the photoconductor reference position mark is detected, in other words, based on the detected photoconductor reference position, Since the color misregistration correction value is created, an image is written based on the detection timing of the photoconductor reference position also in the case of color misregistration correction.
[0091]
Specifically, when the image formation is started, the measured color shift correction value Dn is called from the memory 121 (step S201), and the color shift correction value Dn at the leading end of the image is converted into the timing control correction value and the beam position correction value. Decompose (step S202). Then, the sensor control circuit 130 detects the reference position of the photosensitive drum 10C based on the detection output of the photosensitive member reference position detection sensor 24 (step S210), and writes based on the color misregistration correction value obtained in the routine of FIG. Is started, and image formation is executed (step 203). Since the amount of color misregistration after the leading end of the image changes smoothly without abrupt change, color misregistration correction is performed by correcting the beam position to form an image. As described above, the color misregistration correction value at the leading end of the image can be decomposed, and the image can be formed at the corrected image position from the time when the reference position of the photosensitive drum 10 is detected. Then, the image forming is executed by performing the color shift correction.
[0092]
As described above, according to the present embodiment, the reference position of the photosensitive drum 10 is detected, the color misregistration correction pattern PN formed based on the reference position of the photosensitive drum 10 is detected, Since misregistration correction is performed, highly accurate color misregistration correction becomes possible.
[0093]
In addition, each unit and each process, which are not particularly described, have the same configuration and function as the first embodiment.
[0094]
3. Third embodiment
3.1 Schematic configuration and control configuration of device
In the present embodiment, as shown in FIG. 20, a belt reference position mark 40 is provided on the intermediate transfer belt 11 in the first embodiment, and the belt reference position mark 40 is detected by a belt reference position detection sensor 39 to perform color misregistration. The correction is performed, and the only difference is that the control is performed based on the sensor output of the belt reference position mark 40 and the belt reference position detection sensor 39, and the other components are the same as in the first embodiment. The same reference numerals are given to the respective units, and the duplicate description will be omitted.
[0095]
FIG. 20 is a diagram schematically illustrating a rotation drive mechanism of the photosensitive drums 10Y, 10C, 10M, and 10K and the intermediate transfer belt 11 of the image forming unit 2 according to the present embodiment. As can be seen from FIG. 20, in the rotary drive mechanism of the first embodiment shown in FIG. 9, a belt reference position mark 40 is provided on the intermediate transfer belt 11 and a belt reference position detection sensor is provided on the housing side of the image forming unit 2. 39 are provided. Further, a belt reference position detection sensor 39 is provided as shown in a block diagram showing a control configuration for performing the position shift correction control in FIG. The belt reference position detection sensor 39 is controlled by the sensor control circuit 130, and the sensor output is input to the sensor control circuit 130, and is controlled as shown in FIGS.
[0096]
In the block diagram shown in FIG. 22, the belt reference position detection sensor 39 is added to the control configuration for performing the position shift correction control shown in FIG. 12 in the first embodiment. Are denoted by the same reference numerals, and overlapping description will be omitted.
[0097]
As described above, the relationship between the rotation angle θ from the exposure to the transfer position and the number of rotations of the driving element is set in order to reduce the AC color registration deviation due to the rotation speed fluctuation of the photosensitive drum 10.
(1) Transfer position interval = integer multiple of the distance between exposure and transfer position
{Circle around (2)} Rotation angle θ from exposure to transfer position = motor rotates an integer
(3) Rotation angle from exposure to transfer position θ = idler rotates integer
By setting the following three conditions, and satisfying these three conditions, the period of the rotation unevenness of one rotation of the drum drive motor 19 and the speed fluctuations of the motor gear 20 and the idler gears 22a and 22b are synchronized between the exposure and the transfer. Does not cause color misregistration. However, the photoconductor gear 21 alone cannot be synchronized because it is longer than the period between the exposure and the transfer, causing the AC color registration misalignment. However, by disposing each of the photoconductor gears 21 with the same components and having the same phase and amplitude, the displacement of the AC component position can be eliminated.
[0098]
On the other hand, for driving the intermediate transfer belt 11 or the transfer conveyance belt, a timing belt 32 is stretched around a motor pulley 31 on a drive shaft of a belt drive motor 30 and a drive pulley 33 on a shaft of a belt drive roller 34. It is driven to rotate by transmitting the driving force of the belt drive motor 30. A belt reference position mark 40 for determining the rotation phase of the intermediate transfer belt 11 is provided on the intermediate transfer belt 11 as described above, and the belt reference position detection sensor 39 provided on the housing side detects the intermediate transfer belt. 11 rotation phases are detected. Here, factors causing the speed variation of the intermediate transfer belt 11 include uneven rotation of the belt drive motor 30, eccentricity of the motor pulley 311, eccentricity of the pulley 33 of the belt drive roller, eccentricity of the drive roller, and belt thickness deviation. Can be Here, the color shift is prevented by associating each image forming station pitch L with each drive element as follows.
[0099]
{Circle around (4)} Each image forming station pitch P = belt drive roller circumference × integer multiple
(5) Each image forming station pitch P = integer number of rotations of belt drive motor
By satisfying the above conditions, the rotation unevenness of one rotation of the belt driving motor 30 and the speed fluctuations of the respective pulleys 31 and 33 and the belt driving roller 34 are color-synchronized between the respective image forming stations, and thus the color is changed. There is no gap. The image forming station pitches P are as shown in FIG.
[0100]
FIG. 21 is a graph in which a color misregistration detection pattern is formed at a time when the belt reference position mark 40 is detected by the belt reference position detection sensor 39 and the AC color registration misregistration is measured by the color misregistration detection sensor 38. In this embodiment, the deviation amount of the cyan image is shown with reference to black K. Thus, it can be seen that the color misregistration is caused by the fluctuation of the cycle of the intermediate transfer belt 11 for one rotation. Note that the color misregistration DC color registration misalignment may also be superimposed.
[0101]
3.2 AC color registration deviation due to belt thickness deviation
2. Description of the Related Art Conventionally, a so-called belt body such as a transfer material transport belt and an intermediate transfer belt has been formed into an endless belt body having a seam by connecting sheet materials. However, since an image cannot be formed at the seam, there is a tendency to produce and use a seamless belt body having no seam from the viewpoint of improving the productivity of image formation. For example, in a belt body manufactured by a method of casting and firing a raw material solution in a rotary mold called a centrifugal molding method, the thickness in the circumferential direction of the belt body is likely to be uneven due to limitations in the manufacturing method. This uneven thickness is not an unevenness that repeats the thick and thin over and over in the circumferential direction many times, but often appears in a sine wave shape in the circumferential direction.
[0102]
When a belt having such a thickness deviation is used for a tandem transfer member, for example, the diameter of the driving roller of the belt is D (mm), the thickness of the belt is T (mm), and the image forming speed is V (mm / sec). Then, the diameter of the belt neutral surface (diameter of the pitch circle) is D + T (mm), and the distance between each image forming unit is N × π × (D + T), where N is an integer. Therefore, when the size of the apparatus is reduced to a minimum, the distance between the image forming units is π × (D + T) (mm).
[0103]
Assuming that the belt thickness deviation is ΔT, the fluctuation amount of the image forming speed is:
(ΔT) / (T + D) × V (mm / sec) (1)
It is.
[0104]
Normally, since a full-color image is formed by four image forming units, the distance between the farthest image forming units is 3 × π × (T + D) (mm).
3 × π × (T + D) / V (second) (2)
It takes time.
[0105]
Therefore, the amount of image misregistration caused by belt and roller wear can be calculated by multiplying Expressions (1) and (2) between the most distant image forming units.
3 × π × (ΔT) (3)
It becomes.
[0106]
That is, even when the belt thickness deviation is 10 μm, the color shift amount reaches about 94 μm from the equation (3), and a shift exceeding two pixels when the resolution is 600 dpi repeats every belt period. It can be seen that the AC color registration shift occurs (see FIG. 21).
[0107]
3.3 Creating color shift correction values
FIG. 23 is a flowchart showing a processing procedure for creating a color misregistration correction value according to the present embodiment.
[0108]
In this routine, a process of detecting a belt reference position (step S130) is provided between steps S101 and S102 in the flowchart of FIG. 13 in the first embodiment, and a belt reference position mark is detected by the belt reference position detection sensor 39 described above. The color shift correction pattern PN is written at the time (or based on this time) when the position 40 is detected (step S102), and the color shift detection pattern 38 is detected by the color shift detection sensor 38 to create a color shift correction value. Here, the respective processing steps except for the step S120 are the same as those of the above-described first embodiment, and thus the duplicated description will be omitted.
[0109]
3.4 Correction of color shift during image formation
FIG. 24 is a flowchart showing a processing procedure for correcting a color shift in the third embodiment. In this flowchart, the belt reference position detecting process (step S220) is performed between step S202 and step S203 in the flowchart of FIG. 14 in the first embodiment, and the other processing steps are performed in the first embodiment. Same as the form. That is, after the color shift correction value Dn is created as described above, the color shift is corrected using the color shift correction Dn to form an image. In this embodiment, as described above, the belt reference position mark 40 is detected by the belt reference position detection sensor 39, and the color misregistration is corrected at the time when the belt reference position mark 40 is detected, in other words, based on the detected belt reference position. Since the values are created, the image is written based on the detection timing of the belt reference position also in the case of correcting the color misregistration.
[0110]
Specifically, when the image formation is started, the measured color shift correction value Dn is called from the memory 121 (step S201), and the color shift correction value Dn at the leading end of the image is converted into the timing control correction value and the beam position correction value. Decompose (step S202). Then, the sensor control circuit 130 detects the reference position of the intermediate transfer belt 11 based on the detection output of the belt reference position detection sensor 39 (Step S220), and writes based on the color misregistration correction value obtained in the routine of FIG. The process starts and image formation is performed (step 203). Since the amount of color misregistration after the leading end of the image changes smoothly without abrupt change, color misregistration correction is performed by correcting the beam position to form an image. In this manner, the color misregistration correction value at the leading end of the image can be decomposed, and an image can be formed at the corrected image position from when the reference position of the photosensitive drum 10 is detected. Then, the image forming is executed by performing the color shift correction.
[0111]
As described above, in the decomposition in step S202, the amount of color shift at the leading end of the image is divided by a value corresponding to one line interval to obtain "quotient" and its "remainder". The remainder is input to the beam position control circuit 210. In other words, "quotient" corresponds to writing timing correction, and "remainder" corresponds to beam position correction. Therefore, when decomposing in the example of FIG. 21, when the resolution (writing density) is 600 dpi, the dot pitch is approximately 42 μm. Therefore, when 150 μm is divided by the dot pitch 42 μm,
150 μm / 42 μm = 3 remainder 24
It becomes. Therefore, 126 μm for 3 dots is processed by the timing control circuit 230, the remaining 24 μm is processed by the beam position control circuit 210, the former modulates the LD 61 b, and the latter drives the beam moving motor 70 to reduce color misregistration. to correct. 24 μm corresponds to 12 steps of the beam position moving motor 70. As described above, by performing the timing control and the beam position control in parallel, it is possible to quickly and accurately correct the writing position.
[0112]
As described above, according to the present embodiment, the reference position of the intermediate transfer belt 11 is detected, the color misregistration correction pattern PN formed based on the reference position of the intermediate transfer belt 11 is detected, and the Since misregistration correction is performed, highly accurate color misregistration correction becomes possible.
[0113]
In addition, each unit and each process, which are not particularly described, have the same configuration and function as the first embodiment.
[0114]
4. Fourth embodiment
In this embodiment, the beam irradiation position adjusting mechanism in the first to third embodiments is replaced with a translation mechanism from a rotation mechanism, and other components are the same as those in the first to third embodiments. Since it is configured, duplicate description will be omitted.
[0115]
FIGS. 25 to 27 are views for explaining the fourth embodiment. FIG. 25 is a front view of an essential part showing an LD unit, its supporting mechanism and moving mechanism, and FIG. FIG. 27 is a side view of a guide rail constituting a support mechanism. As shown in FIG. 25, the LD unit 61 ′ according to the present embodiment includes a pair of parallel guide rails 61h extending in the sub-scanning direction (vertical direction in the figure) instead of the rotation center shaft 61f shown in FIG. 61d is movably supported in the sub-scanning direction. Also in this case, the arm 61e is driven by the beam position moving motor 70. The LD unit 61 'moves in parallel with the sub-scanning direction along the guide rail 61h according to the rotation of the beam position moving motor 70. Also in the case of this embodiment, the LD unit 61 'moves so that the irradiation position coincides with the mirror surface 62b of the polygon mirror 62 as shown in FIG. Therefore, the curvature R of the parallel rail 61h is set such that the parallel rail 61h moves on an arc centered on the coincident point of the mirror surface 62b as shown in FIG.
[0116]
Also in this embodiment, the lead screw 71 is screwed into the female screw 61i formed on the arm 61e and is driven by the beam position moving motor 70. However, the arm 61e is omitted and the central portion of the holding member 61d ( (Between the parallel rails 61h). That is, as long as the attitude of the holding member 61d is restricted by the parallel rail 61h, the parallel movement is possible regardless of the position where the lead screw 71 is engaged or screwed.
[0117]
In addition, each unit not particularly described is configured and functions equivalently to those of the above-described first to third embodiments.
[0118]
In the first to fourth embodiments, a tandem type color printer (including a copying machine) is exemplified. However, in a monocolor (black and white) image forming apparatus, a magnification error deviation in the sub-scanning direction is reduced. Also applicable to cases.
[0119]
5. Other embodiments
As mentioned before, other methods include, for example, a method of displacing a turning mirror 69 in an optical writing device to displace a beam irradiation position, and a method of displacing a sheet glass on the upstream side of the polygon mirror 62 where the laser beam L is incident. There is a method of inserting an optical component such as a spear prism and changing the angle or moving the position. In addition, there is a method of deflecting a beam by an acousto-optic element, an electro-optic element, or a liquid crystal.
[0120]
(1) FIG. 28 shows an example of a method of displacing or rotating the return mirror 69 shown in FIG. 4 to displace the beam irradiation position. In FIG. 28, the angle of the folding mirror 69 is changed to change the beam irradiation position on the photoconductor 10. With this configuration, since the optical path α is relatively long, the beam irradiation position Δβ largely moves with respect to the angle change Δθ of the turning mirror 69. Therefore, the cost is low and the optical characteristics are good, but the control is inferior.
[0121]
(2) FIG. 29 shows an example in which the prism PRM is inserted into the optical path L, and the prism PRM is moved to change the beam irradiation position on the photoconductor 10. In this example, the beam irradiation position is changed by moving the prism PRM in a direction orthogonal to the optical path L. When a beam is incident on the oblique side of a triangular prism PRM as shown in FIG. 29 and exits from a plane perpendicular to the optical path L, moving the prism PRM upward in the figure moves the beam downward as indicated by the dotted line. I do.
[0122]
(3) FIG. 30 shows an example in which a glass plate GRS is inserted into the optical path L, and the beam irradiation position on the photoconductor 10 is changed by changing the inclination angle of the glass plate GRS with respect to the optical path L. In this example, when the inclination angle of the glass plate GRS with respect to the optical path L is increased, the beam moves in a direction in which the inclination is increased (a downward direction indicated by a dotted line in the figure).
[0123]
When the optical component is inserted into the optical path L and the beam is moved in this way, the control is excellent, but the optical path is changed by changing the optical path length passing through the glass, which affects the beam diameter and the like. There is a possibility, and a prism or the like increases the cost.
[0124]
{Circle around (4)} FIG. 31 shows that the acousto-optic element SOE is inserted into the optical path L and driven by the drive control circuit SOEC at a higher harmonic to change the beam position. The acousto-optic device SOE is made of LiNbO ₃ An interdigital electrode is vapor-deposited and driven by harmonics. This example is suitable for quick position control, but the cost is unavoidable. The beam may be deflected by an electro-optical element or a liquid crystal instead of the acousto-optical element SOE. The electro-optical element deflects the beam using the photoelastic effect, and the liquid crystal deflects the beam using the light diffraction phenomenon. Each of them is suitable for quick position control similarly to the acousto-optic element SOE, but is expensive and disadvantageous in cost as compared with other examples.
[0125]
In an image forming apparatus that forms an image by irradiating a photoconductor with a laser beam, if the color misregistration is corrected by controlling the beam irradiation position for color misregistration due to fluctuations in the rotation speed of the photoconductor or belt, etc. Therefore, it is necessary to control the beam irradiation position smoothly and slowly by reducing the distance. This is because if the beam position is instantaneously moved to a large extent, the distance between scanning lines will change greatly, resulting in an image such as a white spot. From such a point of view, the method (4) is not suitable for color misregistration correction as in the present invention, and the cost increases. It is considered that the method (1) has a problem in the correction accuracy as described above, and it is also difficult to solve a problem such as white spots. In the methods (2) and (3), the accuracy control is good, but there is a concern that the optical characteristics are affected as compared with the first to fourth embodiments of the present application, and the cost is higher than that of the first embodiment. .
[0126]
As described above, the cause of the color misregistration is the rotational speed fluctuation of the photoconductor and the transfer belt. However, since the fluctuation itself has periodicity and good repeatability, the speed fluctuation is measured in advance. The color misregistration correction value is calculated by the color misregistration amount calculation circuit 110 and then stored in the memory 121. When a print command is output, the color misregistration correction can be performed using the correction value. The stored color misregistration correction value can be confirmed from the operation panel or the printer driver, and if the user or service person can change the color misregistration correction value, more precise color misregistration correction can be performed. It becomes possible.
[0127]
【The invention's effect】
As described above, according to the present invention, it is possible to correct the misregistration of each color image in the sub-scanning direction at the same rotation phase during the formation of a latent image, so that the color misregistration can be corrected with higher accuracy. become.
[0128]
Further, since the color misregistration can be corrected with high accuracy, it is possible to form a high quality image.
[0129]
Further, since a large displacement and a small displacement can be corrected simultaneously and in parallel by different methods, the correction process can be quickly performed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically showing a color laser printer as an image forming apparatus according to a first embodiment.
FIG. 2 is a plan view of the optical writing (exposure) device in FIG.
FIG. 3 is a sectional view showing a schematic configuration of an optical writing (exposure) device in FIG.
FIG. 4 is a sectional view showing a schematic configuration of another example of the optical writing (exposure) device in FIG.
FIG. 5 is a diagram illustrating a configuration example in which a laser beam irradiation position is displaced in a sub-scanning direction.
FIG. 6 is a diagram illustrating a relationship among an LD unit, a polygon mirror, an optical axis, and a rotation center axis.
FIG. 7 is a front view of the beam irradiation position adjusting device when the LD unit is viewed from a laser light emission side.
8 is an explanatory diagram showing a beam position on the photoconductor surface when the beam position of the laser beam on the photoconductor surface is moved by the beam irradiation position adjusting device of FIG. 7;
FIG. 9 is a diagram schematically illustrating a rotation drive mechanism of a photosensitive drum and an intermediate transfer belt of the image forming unit according to the first embodiment.
FIG. 10 is a diagram illustrating an example of a color misregistration detection pattern formed on an intermediate transfer belt.
FIG. 11 is a diagram showing a result of forming a color misregistration detection pattern and measuring an AC color registration misregistration by a color misregistration detection sensor, showing a misregistration amount of a cyan image with reference to black.
FIG. 12 is a block diagram illustrating a control configuration for performing misregistration correction control according to the first embodiment.
FIG. 13 is a flowchart illustrating a procedure of a color misregistration correction value creation process according to the first embodiment.
FIG. 14 is a flowchart illustrating a processing procedure of a color misregistration correction process during image formation according to the first embodiment.
FIG. 15 is a diagram schematically illustrating a rotation driving mechanism of a photosensitive drum and an intermediate transfer belt of an image forming unit according to a second embodiment.
FIG. 16 is a diagram showing a result of forming a color misregistration detection pattern and measuring an AC color registration misregistration by a color misregistration detection sensor, showing a misregistration amount of a cyan image with reference to black.
FIG. 17 is a block diagram illustrating a control configuration for performing misregistration correction control according to the second embodiment.
FIG. 18 is a flowchart illustrating a procedure of a color misregistration correction value creation process according to the second embodiment.
FIG. 19 is a flowchart illustrating a procedure of a color misregistration correction process during image formation according to the second embodiment.
FIG. 20 is a diagram schematically illustrating a rotation driving mechanism of a photosensitive drum and an intermediate transfer belt of an image forming unit according to a third embodiment.
FIG. 21 is a diagram showing a result of forming a color misregistration detection pattern and measuring an AC color registration misregistration by a color misregistration detection sensor, showing a misregistration amount of a cyan image with reference to black.
FIG. 22 is a block diagram illustrating a control configuration for performing misregistration correction control according to a third embodiment.
FIG. 23 is a flowchart illustrating a procedure of a color misregistration correction value creation process according to the third embodiment.
FIG. 24 is a flowchart illustrating a procedure of a color misregistration correction process during image formation according to the second embodiment.
FIG. 25 is a front view of a beam irradiation position adjusting device according to a fourth embodiment.
26 is an explanatory diagram showing a beam position on the photoconductor surface when the beam position of the laser beam on the photoconductor surface is moved by the beam irradiation position adjusting device of FIG. 25;
FIG. 27 is a side view of a main part of the guide rail in FIG. 25.
FIG. 28 is a diagram illustrating an embodiment in which the beam irradiation position on the photosensitive member is changed by changing the angle of the folding mirror.
FIG. 29 is a diagram showing an embodiment in which the beam irradiation position on the photoconductor is changed by changing the position of the prism.
FIG. 30 is a diagram showing an embodiment in which the beam irradiation position on the photoconductor is changed by changing the angle of the glass plate.
FIG. 31 is a diagram illustrating an embodiment in which the acousto-optic device is driven by a harmonic to change the beam irradiation position on the photoconductor.
[Explanation of symbols]
1 color laser printer (image forming device)
2 Imaging device
5 Transfer unit
6 Exposure unit (optical writing device)
7 Cleaning unit
8 Charging unit
9 Developing unit
10, 10Y, 10C, 10M, 110K Photoconductor drum
10a Photoconductor surface
11 Intermediate transfer belt (intermediate transfer body)
19 Drum drive motor
20 Drive motor gear
21 21Y, 21C, 21M, 21K Photoconductor gear
22a, 22b Rotating connection gear (idler gear)
23 Photoconductor reference position mark
24 Photoconductor reference position detection sensor
30 Belt drive motor
34 belt drive roller
35 Pressure roller
36 driven roller
38 Color shift detection sensor
39 belt reference position detection sensor
40 Belt reference position mark
61, 61Y, 61M, 61C, 61K, 61 'LD unit (laser light source)
61a Semiconductor laser (LD)
61b Collimating lens (coupling optical system)
61d holding member (base)
61e arm
61f rotation center axis
61g laser beam axis
61h guide rail
61i female screw
62 polygon mirror
62b polygon surface
63 Imaging optical system
65 aperture
66 cylinder lens
69 mirror
70 Beam position moving motor
71 Lead Screw
100 Registration Controller
110 Color shift amount calculation circuit
120 Color shift correction value calculation circuit
121 memory
130 Sensor control circuit
140, 140Y, 140M, 140C Counter
200 System Controller
210 Beam position control circuit
220 motor driver
230 Write timing control circuit
240 LD modulation circuit
PN color shift detection pattern

Claims (21)

When the latent image written on the image carrier by the optical writing means is visualized, and the visualized images having different colors are directly or indirectly transferred onto a moving body to form an image, In a color shift correction method for correcting a color shift due to an image position shift,
While the light writing unit irradiates the light beam to form a latent image, the irradiation position of the light beam emitted from the writing unit is adjusted in the sub-scanning direction to correct the color shift between the colors. A color misregistration correction method characterized in that: The adjustment of the irradiation position of the light beam in the sub-scanning direction is performed based on a result of reading a pattern written on the image carrier before the adjustment is started and for detecting a visualized color shift. The color misregistration correction method according to claim 1, wherein: 3. The color misregistration correction method according to claim 2, wherein a timing of writing the pattern is set based on a detection timing of a reference point provided on the image carrier. 3. The color misregistration correction method according to claim 2, wherein the timing of writing the pattern is set based on the timing of detecting a reference point provided on the intermediate transfer member. 2. The method according to claim 1, wherein the adjustment in the sub-scanning direction includes a step of correcting a writing timing of an optical writing unit and a step of correcting a beam position of a light beam, and both steps are performed in parallel. Color shift correction method. The step of correcting the write timing corrects a portion corresponding to a quotient obtained by dividing the positional deviation amount by the dot pitch,
6. The method according to claim 5, wherein the step of correcting the beam position corrects a portion corresponding to a remainder obtained by dividing a positional shift amount by a dot pitch. An optical writing device that has a plurality of optical writing units that irradiate a light beam to an image carrier based on input image information, and performs optical writing for forming a plurality of colors of images.
Optical writing is performed on the image carrier, and while forming a latent image, the irradiation position of the light beam on the image carrier irradiated from the optical writing unit is matched when the images of the respective colors are superimposed. An optical writing device, further comprising an adjusting means for adjusting the distance in the sub-scanning direction. The optical writing means includes a laser light emitting element and a coupling optical system,
8. The apparatus according to claim 7, wherein the adjusting unit includes a holding member that holds the laser light emitting element and the coupling optical system integrally, and a driving mechanism that moves the holding member in a sub-scanning direction. Optical writing device. The holding member is rotatably supported on a support shaft in an eccentric state with respect to the optical axis of the light beam, in an optical housing that holds an optical deflector and another optical element that irradiates the image carrier with a light beam. 9. The optical writing device according to claim 8, wherein: 10. The optical writing device according to claim 9, wherein the driving mechanism drives the holding member to rotate about the support shaft. The eccentric state of the two axes is set such that an optical axis of the light beam and a rotation center axis of a holding member substantially coincide with each other at a light beam deflection position of the optical deflector. Optical writing device. The holding member is provided with a guide member parallel to the sub-scanning direction of the image carrier in an optical housing that holds an optical deflector and another optical element that irradiates the image carrier with a light beam. 9. The optical writing device according to claim 8, wherein the optical writing device is movably supported along the guide member. 13. The optical writing device according to claim 12, wherein the driving mechanism moves the holding member in parallel along the guide member. 13. The optical writing device according to claim 12, wherein a curvature of the guide member is set such that an optical axis of the light beam when moved is substantially coincident with a light beam deflection position of the light deflector. An image having different colors is formed by at least one image forming means having an image carrier, and the images having different colors formed by the image forming means are directly or indirectly transferred onto a moving body to perform image formation. In the image forming apparatus to be performed,
An image forming apparatus comprising the optical writing device according to any one of claims 7 to 14. Forming a plurality of patterns for detecting the color shift of each color on the moving body, further comprising a color shift amount detecting means for detecting the color shift amount based on the formed pattern,
16. The image forming apparatus according to claim 15, wherein the adjustment unit adjusts based on the color shift amount detected by the color shift amount detection unit to correct the color shift. A reference position mark provided for detecting a rotation phase of the image carrier,
Detecting means for detecting the reference position mark;
Calculating means for detecting a color shift amount of each color on the moving body based on a detection position of the reference position mark, and calculating a color shift correction value corresponding to each color;
And adjusting the light beam irradiation position on the image carrier corresponding to each color by the adjusting means based on the detected reference position mark and the calculated plurality of color misregistration correction values during image formation. The image forming apparatus according to claim 15, wherein the shift is corrected. A reference position mark provided for detecting a rotational phase on the moving body,
Detecting means for detecting the reference position mark;
Calculating means for detecting a color shift amount of each color on the moving body based on a detection position of the reference position mark, and calculating a color shift correction value corresponding to each color;
And adjusting the light beam irradiation position on the image carrier corresponding to each color by the adjusting means based on the detected reference position mark and the calculated plurality of color misregistration correction values during image formation. The image forming apparatus according to claim 15, wherein the shift is corrected. A writing timing control circuit that controls a timing of irradiating a light beam on each image carrier based on the reference position mark of the image carrier and the plurality of calculated color misregistration correction values; 19. The image forming apparatus according to claim 17, further comprising a beam position control circuit for controlling an irradiation position. A quotient obtained by dividing the displacement amount by the dot pitch is input to the write timing control circuit,
The write-to-MIG control circuit modulates the laser light emitting element based on the quotient,
The remainder obtained by dividing the displacement amount by the dot pitch is input to the beam position control circuit,
20. The method according to claim 19, wherein the beam position control circuit moves the optical housing based on the remainder. A memory for storing the plurality of color misregistration correction values,
Reading means for reading a plurality of stored color misregistration correction values;
The image forming apparatus according to claim 17, further comprising:

Images